This invention relates to confined explosive separation systems; and more particularly, to the separation joint portion of the explosively operated, linear charge, separation system most commonly observed separating space boosters from payload portions during space exploration.
Explosive separation systems are typically used for stage and payload separation, door and fairing jettison and shroud removal in various space applications. Basically, two different types of separation systems are used. Point separation systems utilize explosive bolts or nuts while linear separation systems utilize flexible linear shaped charge (FLSC) or mild detonating cord (MDC). Point separation systems employ rows of bolts, each of which is individually fired, or V-band clamp joints (Marman type clamp) using an explosive bolt to close the clamp. Of course, the sections to be joined must terminate in a shape to match the inner V section of the clamp. V-band clamp joints are structurally inefficient, resulting in understrength and overweight structure when used to support large diameter, heavyweight spacecraft.
Newer generation spacecraft are larger in diameter and heavier in weight and will not tolerate this structural inefficiency. Hence confined linear explosive separation systems were developed. Although several confined separation systems are in existence, they do not represent an optimum in the performance versus weight aspect.
One technique for accomplishing linear separation is taught in U.S. Pat. No. 3,373,686 to Blain, et al. Blain teaches enclosure of MDC in an elastomeric sheath (as taught in U.S. Pat. No. 3,311,056 to G. A. Noddin) which is confined between specially designed structure. The explosive products expand transmitting force through the medium of the elastomer to the structure and finally cause severance. This joint clearly fails in combined bending and tension as a result of the span between the rows of bolts, the mid location of the break slot, and the spacing between bolts. The primary failure is not in shear, because there is no rigidity to any portion of the joint.
Another technique is taught in U.S. Pat. No. 3,362,290 issued to W. F. Carr, et al. and assigned to the same assignee as this application. Carr teaches the piston and chamber combination with a linear explosive contained within two concentric stainless steel tubes which run the length of the joint. The stainless steel tubes are in turn confined within a thin walled elastomeric bellows which is in turn inflated by the hot gases of the explosive. The gases pass through a line of holes in each tube, oriented such that the holes in the two tubes are 180.degree. apart to prevent perforation of the bellows by the fast moving hot particles from the exploding MDC. The piston and chamber are attached, one each, to the two parts of the contiguous sections to be separated by a line of retaining rivets. The hot gasses inflate the bellows, which in turn shears the retaining rivets and thrusts the two halves of the joint apart to provide the initial step in the separation operation. This is a thrusting joint and does not sever structure to achieve the separation, only a row of rivets. Further, this joint is very heavy and has very poor load carrying ability prior to separation.
Another approach to confined linear explosive separation systems is that taught by U.S. Pat. No. 3,486,410 issued to Drexelius, et al. and again assigned to the same assignee as this invention. This reference teaches a separation system based on tube expansion. Explosive cords are supported in an extruded plastic part which just fits inside of a flattened steel tube. When the explosive is fired, it produces gases which expand the flattened tube to produce the necessary displacement for a continuous structural severance and separation. The flattened tube is contained in a cantilevered clamping means by a single row of bolts which produces poor rigidity. Much of the work produced by the explosive is absorbed in bending and deflecting the clamp. There is some teaching of orienting the break slot to the location of the linear explosive. However, because of the structural arrangement, both the clamp and the parent structure being severed see mostly tension and bending and produces inefficient deflection prior to separation. Basically, any joint which is bolted in close proximity to the break line suffers from the fact that more energy (and displacement at the load point) is required between the bolts than at the bolts. Hence, the separation action is not continuous as it is with the one-piece design of the present invention.
Finally, U.S. Pat. No. 3,698,281 issued to O. E. Brandt, et al., also teaches an expanding tube separation joint quite similar to the '410 patent discussed above. However, this reference teaches a pair of explosive cords, spaced side by side in an elastomer and contained in a flattened steel tube. Further, the '281 patent teaches a pair of splice plates or doublers, one on either side and abutting the two sections to be joined with a space therebetween. The space contains the explosive cord in the flattened tube while the doublers are attached to the sections to be joined by a row of bolts at each end of the splice plates. Break slots are provided at the midpoint of each splice plate and located between the explosive cords. This reference suffers from the same deficiencies as the '410 patent in that the splice plates fail primarily in bending and tension as opposed to shear. The reason for this type of failure is the span subjected to the explosive force is too large, insufficient rigidity in the joint, and wrong location of the break slot. Bolt attachments are inefficient from a rigidity standpoint because of the spacing between bolts.
In summary, the expanding-tube type separation joints discussed above do not take optimum advantage of the explosive energy or inherent structural properties of the joint. These joints break at the end of the tube stroke when explosive forces are the least, and are designed to fail in tension, which is the materials strongest property.
It is an object of this invention to provide a separation joint which breaks at the separation plane in shear, which takes advantages of the materials weakest properties. It is a further object of the invention to provide a joint which breaks during the initial expansion of the tube enclosing the explosives, when explosive forces are at their greatest. Still further objects of the invention are to provide a light-weight, non-contaminating, structurally efficient separation joint which results in a continuous fracture as opposed to the discontinuous fracture of the bolted joints of the prior art.